Various organometallic precursors are used to form thin metal films. A variety of techniques have been used for the deposition of thin films. These include reactive sputtering, ion-assisted deposition, sol-gel deposition, CVD (also known as metalorganic CVD or MOCVD), and ALD (also known as atomic layer epitaxy). The CVD and ALD processes are being increasingly used as they have the advantages of good compositional control, high film uniformity, good control of doping, and, significantly, they give excellent conformal step coverage on highly non-planar microelectronics device geometries.
CVD is a chemical process whereby precursors are used to form a thin film on a substrate. In a typical CVD process, the precursors are passed over a substrate (e.g., a wafer) in a low pressure or ambient pressure reaction chamber. The precursors react and/or decompose on the substrate surface creating a thin film of deposited material. Volatile by-products are removed by gas flow through the reaction chamber. The deposited film thickness can be difficult to control because it depends on coordination of many parameters such as temperature, pressure, gas flow volumes and uniformity, chemical depletion effects, and time.
ALD is also a method for the deposition of thin films. It is a self-limiting, sequential, unique film growth technique based on surface reactions that can provide precise thickness control and deposit conformal thin films of materials provided by precursors onto substrates of varying compositions. In ALD, the precursors are separated during the reaction. The first precursor is passed over the substrate producing a monolayer on the substrate. Any excess unreacted precursor is pumped out of the reaction chamber. A second precursor is then passed over the substrate and reacts with the first precursor, forming a second monolayer of film over the first-formed monolayer of film on the substrate surface. This cycle is repeated to create a film of desired thickness. ALD film growth is self-limiting and based on surface reactions, creating uniform depositions that can be controlled at the nanometer-thickness scale.
Thin films have a variety of important applications, such as nanotechnology and fabrication of semiconductor devices. Examples of such applications include, conductive films, high-refractive index optical coatings, corrosion-protection coatings, photocatalytic self-cleaning glass coatings, biocompatible coatings, dielectric capacitor layers and gate dielectric insulating films in field-effect transistors (FET), capacitor electrodes, gate electrodes, adhesive diffusion barriers and integrated circuits. Thin films are also used in microelectronics applications, such as the high-κ dielectric oxide for dynamic random access memory (DRAM) applications and the ferroelectric perovskites used in infra-red detectors and non-volatile ferroelectric random access memories (NV-FeRAMs). The continual decrease in the size of microelectronics components has increased the need for the use of such thin films.
Oxides and nitrides of molybdenum have numerous important applications. For example, molybdenum dioxide (MoO2) displays unusual metal-like conductivity and has found applications in hydrocarbon oxidation catalysts, solid oxide fuel cell (SOFC) anodes, and high capacity reversible lithium ion battery (LIB) anodes. See, for example, Ellefson, C. A., et al., J. Mater. Sci. 2012, 47, 2057-2071. Molybdenum trioxide (MoO3) exhibits interesting electrochromic and catalytic properties and has found applications in nano-structured gas sensors and in solid-state lithium ion batteries. See, for example, Diskus, M., et al., J. Mater. Chem. 2011, 21, 705-710. Finally, thin films of transition metal nitrides have long been known to generally possess good mechanical and chemical stability. Films of molybdenum nitride (MoN and/or Mo2N) have been studied for applications including microelectronic diffusion barriers, high-Tc superconductors, and tribological and protective coatings. See, for example, Miikkulainen, V., et al., Chem. Mater. 2007, 19, 263-269.
Theopold, K. H., et al. report the synthesis and isolation of the Mo complex CpMo(CO)2(η3-2-methylallyl). Science of Synthesis, 2003, 229-281.
Green, J., et al. report the synthesis and isolation of the Mo complex, (C6H6)Mo(η3-allyl)2. J. Chem. Soc., Dalton Trans. 1973, 1403-1408 and J. Chem. Soc., Dalton Trans. 1973, 1952-1954.
Current molybdenum precursors for use in CVD and ALD do not provide the required performance to implement new processes for fabrication of next generation devices, such as semiconductors. For example, improved thermal stability, higher volatility, increased vapor pressures, and increased deposition rates are needed.